Transmission circuits



R. c. MATHES TRANSMISION CIRCUITS Filed Nov. 1-, 1919 mvemqrz um n1 H Hw m H Ill" mum

enema May as, ice;

.a citizen of the United States,

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near 0. marries, or NEW roam-1r. Y., ASSIGNOR r0 weer-nan nnnornrcoomanr,

mew rams.

INCORPORATED, OF NEW YORK, N. Y., A CORPORATION NEW YORK.

rnsnsmssion omcurrs.

Application filed November 21,..19i9l l$ eria1 Ho. 339,740.

C; MATHES, residin at New York, in the county of Bronx, tate of NewYork, .have invented certainnew and useful Improvements'in TransmissionBe it knownthat I, Rosana Circuits, of which the following is afull,

clear, concise, and exact, description.

This invention relates to transmission circuits and more particularly itrelates to two-way repeating systems.

As is well known in the art, it is frequently found desirable to providea repeating or amplifying system between two transmission lines. In oneform such a repeating system may have, the'transmission linesar'eterminated in a Wheatstone bridge type of circuit; for 'securingtwo-way transmission from unidirectional amplifying systemss As is wellknown, the conjugatecondition of such bridge circuits" is maintained byproviding networks which closely simulate the impedance of the transniission line, or by balancing two similar transmission lines againsteach other. It is further well known in the art that if'a high degree ofconjugacy is notpbtained there is'a critical amount of amplificationbeyond which one cannot go without setting up a local circulation ofenergy in the form of a sustained tone, commonly known as singing. It isevident, therefore, that if any condition exists other than theunbalance between'line and network which causes the transmission ofelectrical energy between the two circuits designed tobe conjugate, sucha con.- dition will further limit the amount of gain which can beobtained from the set.

Ithas been found in practical arrangements of telephone repeaterequipment that the capacites between the primary and secondary windingsofthe transformers employed afiord a path for the transmission of energybetweenthe parts of the circuit presumably conjugate. As thetransmission of such undesired potentials is through a series capacity,it is most' efhcient at high frequencies so that it may even result in asustained singing at an inaudible frequency.

* This result, while not interfering as d rect re, seriously impairs thenormal telephone tiansmission through the circuit and so essitates areduction in ampl fication.

accordance with this invention, this objectionable loss in transmissionefiiciency peatingcoil 13 in a manner now well known of a two-wayrepeater circuit may be overcome by shunting these undesired potentials.throng a low" impedance pathto ground. One way this maybe accomplishedisby grounding one or more neutral points of the repeater system.

This invention will be better understoodby reference 'to the followingdetailed description, taken in' connection with the drawings in whichFig. 1 represents thisinvention embodied in a two-way Q-repeater .systemand Fig. 2represents this invention connected between the coils 6 and 7and coils '8 and 9 are. impressed through a filter 11 upon an amplifier12. The amplified CH1". rents in the output circuit of amplifier 12are-impressed upon outgoingfline 4 by reto the art without anyappreciable part being directed back to the input of repeater .19.. Smilarly incoming currents from. line 4 are impressed by connectionstaken .between windings 14 and 15, and 16 and 17. through a filter 18upon an amplifier 19. The amplified currents of repeater 19 areimpressed upon outgoing line 3. The balancing networks 5 and 20 forlines 3. 3 and 4, 4 respectively may be of any suitable design, forexample they may be of the form disclosed in the Hoyt Patent5.21.167.694 of August. 7, 1915. The preferred form of filters 11 andand 18 is disclosed in the Campbell Patent #1,227,113 of May 22, 191

I 'As pointed out above, a local circulation of power in the.tworhalvesof the repeater circuit other than t'hat due to improper linetransformers in the circuit. For example,

if the control electrode 21 of amplifier 12 were to undergo a change inpotential, this change would be amplified by amplifier 12 so that thewinding 22 of 110 capacity between the primary and" secondrepeating coil13 would acquire a certain potential to ground. Due to the capacitypresent between winding 22 and the other windings of repeating coil 13,all the 'apparatus between repeating coil 13- and the primary oftransformer 25 would therefore I acquire-a certain"potential withrespect to ound. The potential with respect to ground which the primaryof transformer 25 thus has will be transmitted through the ary windingsof this transformer so as to impress a potential on the controlelectrodeof amplifier 19. This amplified potential,

'due to the capacity effect between the primary winding and thesecondary windings of transformer '10, will give all the appa ratuslocated betweenthe secondary of transformer 10 and the primary oftransformer 24 a potential with respect toground. This potential in turnwill be. transmitted through the capacities of transformer 24 to give apotential to'the control electrode of amplifier 12- which potentialwillagainbe amplified by.-amplifier. 12. It is evident that if thereturned impulse is equal to the initial impulse, sustained singing W111be set up. Even if an ihsufiicient amount is fed back in this way toproduce singing, its:

effect may add to unbalanced conditions otherwise present and so furtherlimit the gain which'ma be obtained from the set;

This efi'ect. mig t be called an effective in-v tgrnal unbalance.

' It is to be noted that each repeater, -the secondary of eachinput-transformer, and the primary of each output transformer; areaasymmetrically connected to ground, due to' the grounded connections ofthe cathodes of the repeaters. The secondary of each output transformer,however, together with the filter and the primary winding of each in--put transformer are symmetrically located with respect to ground. Thatis, the potential to ground impressed upon the sec- ,ondary of eachoutput transformer does not create a. current which flows seriallythrough the two side conductors, but the effect is transmitted throughthe side conductors in parallel to' the primary of each inputtransformerq ln other words, the po-' tential. gives rise tolongitudinal currents in this part of the circuit. -This manner of thetransfer of the potential to ground from the output transformer to theinput transformer is therefore such that the high frequency singing setup thereby cannot be prevented by adjusting the constants of filter 11and 18 to cut out the high frequencysinging. These, filters can be madeto cut out, high frequencies only when the currents of the undesiredfrequencies fiow serially through the two side conductors of thecircuit.

One way in which this local circulation of power may be overcome is toground one or more neutral or central points in corresponding parts ofthe apparatusln that part of the repeater circuit which is symmetricallylocated with respect to ground. Thus these midpoints ofthe primary wind-'ings of inputjtransformers 24 and 25 may be connected through a lowimpedance path to ground Withsuch a connection, potentials to groundwhich, for, example, winding 22may acquire, will give a potential toground to the .primary windingof transformer 25 due to the capacitybetween the primary and secondary windings of repeat.- ing-coi1.13, butwhen the midpoint of pri-v mary winding of transformer 25 is connectedtoground, this potential finds a low impedance path. to ground throughthis grounded connection. I s

Similarly if any'potential in the unidirectional path containingrepeater 19 is fed back through the capacity between the windit isdesirable that the grounded connection should be at the central point ofthe primary windings of the transformers. If the loo grounded connectionis not taken, at fsu bstantially the midpoints of the winding, one' ofthe two sides of each path would acquire a higher potential to groundthan the other side, thereby creating an unbalanced condition whichwould allow the local circulation of power which it is desired toeliminate.

"Furthermore an. unbalanced ground would unbalance the telephonecircuits to which such a repeater might be connected without interveningtransformers. a v Another way the local circulation of-power may beovercome is by connecting the midpoints of the gain adjustingpotentiometers- 27 and 28 through a lowimpedance path to.,

ground. If desired, this grounded conned-" tion may be taken throughlargekcondensers- 29iand 30. Thislocal circulation of power may be alsoprevented by connecting between the bridged points of thejwo repeatingcoils 10 and 13, two retardation coils 34 and 35 and bygrounding themidpoints of thesetwo coils. Any potential to grounkLthat the secondaryof repeating coil 13 would acquire due to the potential to ground in theprimary of the repeating coil would be prevented from reaching amplifier19 since the energy' would find a readypath to ground through thegrounded connection of the midpoint of meaeio terminals of the primarywinding of the in-' put transformer 24]; The use of double adjustablecontacts allows the setting of the potentiometer to change withoutinterfering with the symmetrical connection to ground of the leads fromthe midpoints of the threewinding transformer to the input transformer24. If only one adjustable contact instead of two were employed, forexample, to vary the repeater gain, any variation in its position wouldchange the symmetrical connection'to ground through condenser of theterminals of the primary winding of transformer 24, in the case Wherethe only grounded midpoints were the midpoints of the potentiometers.

Several ways have been described above for increasing the transmissionefficiency of the two-way repeater system for eliminating an effectiveinternal unbalance by providing a symmetrical path to ground for thatportion of the repeater apparatus which is floating with respect toground. In any particular case," it may be desirableto employ one of theabove methods inpreference' to the others, or it may be found desirableto employ all the methods in the same circuit.v

Fig. 2 illustrates this invention in connection with a two-way onerepeater system "imwhich balancing networks are eliminated and the onetransmission line is balanced by the other transmission line 51. Located7 between the two lines 50 and 51 are the four windings 52, 53,54 and 55of repeating coil 56. Across the bridged points of these windings areconnections which lead through a filter 57 and the gain adjustingpotentiometer 58 to the primary winding of the input transformer 59.Amplifier 60 has its input terminals connected to the secondary ,oftransformer 59 and has its output terminals connected to the primarywinding of repeating coil 56. With such an arrangement signalsoriginating in either of the two transmission lines will be impressedthrough the filter upo' -the amplifier and the amplified signals will beimpressed back on the two transmission lines by repeatingcoil 56.

As in the repeating system of Fig. 1, the re* peatlng system of Fig. 2may-be freed from any circulation of power, other than that due to lineunbalance, byeither grounding the mid point of gain adjustingpotentiometer 58 or mid point of the primary Winding of the inputtransformer 59, or by grounding the midpoint of the retardation coil 63which is connected across the bridge points.

From the above description it is apparent peater.

that applicants invention is not limited to the particular circuitarrangements above described and that it may be variously modifiedwithout dep'arting'in any way from the spirit of this invention asdefined in the appended claims.

What is claimedv is:

1. A two-way repeating system comprising a uni-directional pathcomprising an amplifier and impedance devices, a symmetricalconnection'to ground for certain of saiddevices, and an asymmetricalconnec tion to. ground for other of said devices.

2. A two-way repeating system comprising a uni-directional pathcontaining a repeater asymmetrically connected to ground,

a transformer, apparatus in said path con-- -nected through saidtransformer to said rerespect to said line conductors and to the inputterminals of said repeater, and a connection to ground from the midpointof said impedance for preujnting output energy from said repeateu frombeing fed back upon the input terminals of said repeater.

5. In an electric system, a two-Way repeating circuit comprising arepeater in each of two unidirectional paths, an output transformer forone of said repeaters and means for preventing energy from the primaryof said transformer from being fed back to the input of said lastmentioned repeater, saidmeans comprising a grounded device symmetricallylocated with respect to the two line conductors forming the electricalpath between said transformer and said last mentioned repeater.

6. A two-way repeating system comprising a repeater in each of twounidirectional paths, an output transformer for one of said repeaters,and means for preventing energy from the primary of said transformerfrom being fed back to the input of said .last mentioned repeater, saidmeans comprising a shunt to ground equally effective for both'of the twoline conductors forming the'electrical path between said transformer andsaid last mentioned re- 7. A two-way repeating system comprising arepeater in each of tWo unidirectional paths, a'n output transformer foroneof said repeaters and means for preventing energv from the primary ofsaid transformer from being fed back to the input of said last mentionedrepeater, said means Comprising an I impedance connected in shuntbetween'the' twolineconductors forming the electrical path between saidtransformer and said last ductors forming the electrical path betweensaid transformer and said last mentioned repeater, said impedance havingconnectedlto ground, p

9. A two-way repeating system comprisits midpoint inga unidirectionalpath for repeating in one direction,- a second unidirectional path forrepeating inthe 'opposite direction, a repeater in each of saidpaths,and means for preventing ener' from one of said.

- paths from being fedackover the other of saidpaths to the repeater insaid first men -tioned path, said -means comprising an impedanceconnected across the two line conductors forming the conducting path insaid system, said impedance having its midpoint sionlines, a two-wayrepeating circuit begrounded, said grounded connection being.

equally effective for the line conductors.

. 10. A two-way repeating system comprising a unidirectional path forrepeating in one direction and a second unidirectional. pathforrepeating in the opposite direction, a repeater in each of said pathsand animpotentials in .either of pedance connected effectively in shuntto the inputterminals of each of said repeaters and having theirmidpoints connected to ground for preventing output energy from one or,

said repeaters from being impressed upon the input terminals of theother of said repeaters. 11 On an electric system two transmiss tweensaid lines, said circuit comprising a balancing network foreach of saidlines, a unidirectional path for repeating in -one direction betweensaid lines, a second unidirectional path for repeating in the oppo sitedirection between said lines, and an impedance connected effectivelyacross the bridge points connecting one of said lines with its balancingnetwork, said impedance having. its midpoint connected to ground,

12. 'In combination, two line sections, an

I artificial line fonbalancing each of said line SGCfilOllS, auni-directional path for repeating in one direction between said-linesections, a

second uni-directional path for repeating inthe opposite direction, arepeater located in each of said paths and having input and output termnals, an impedance, and means tudinalcurrents in said ing frequencies.

comprising a connection to ground frointhe,

-midpoint of said impedance for preventing the local circulation ofpower in-said paths 13. In combination, two line sections, an artificialline for balancing each of said-line sections, a uni-directional pathfor repeating in one direction between said line sections, a seconduni-directional path for repeating in theoppos'ite direction, a.repeater located in each of saidpaths'a'nd having input and out-'- putterminals,;an impedance, and means for i preventing longitudinalcurrents in .said

pathsffrom causing said repeaters tosing.

14. A-xtwo-way repeating system comprisinga-unii-directional pathcontaining a repeater, a wave filter for suppressing certain freguenciesof currents flowing seriallyin sai path, andineans for sup-pressinglongipath of correspond- 15. In combination, an incoming line, a-

uni-directionaLpath associated with said line and comprising a vacuumtube amplifier, a wave filter..1n said path for suppressing certainfrequencies of currents flowing serially in said path, and means betweensaid line and said amplifier for preventing longitudinal currents frombeing impressed upon said amplifier.

16. In combination, an incoming line, a uni-directional path associatedwith said line and comprising means for suppressing certain frequencieswhen they consist of currents flowing serially in said path, and meansfor suppressing certain frequencies in said path when they consist oflongitudinal currents in said path.

17. Atwo-way repeating system comprising a uni-directionalpath-containing a re- 'peater, a wavefilter for preventing currents qflowing serially-in -said path from causing said repeater to-sing, andmeans for preventing longitudinal currents in said path from causingsaid repeater to sing.'

18. A repeating system comprising a Wheatstone bridge network havingfour impedance arms, repeaterinput terminals, re-

peater output terminals, a connection from the midpoint ofthe first andthe second arms of said bridge tonne of said repeater input terminals, aconnection from the midpoint of the third and fourth arms to another of-19. A repeating system comprising a Wlieatstone bridge network havingfour impedance arms, repeater input terminals, re-

peater output terminals, a connection from the midpoint of the first andthe second arms 3 of said bridge to one of said repeater inputterminals, a connection from the midpoint of the third and fourth armstoanother of said repeater input terminals, a connection from the midpointof said first and fourth, arms to a repeater output terminal, aconnection from the midpoint of the second and third arms to ,a secondrepeater output terminal, an impedance effectively in shunt to saidfirst two connections, and a connection to ground from the midpoint ofsaid impedance for preventing the local circulation of power betweensaid output terminals and said'input terminals.

20. A repeating system comprising a VVheatstone bridge networkhaving-four impedance arms,'repeater input terminals, re-

peater outputterminals, a connection from the midpoint of the first andthe second arms of said bridge to one of said repeater input-.terminals, a connection fromthe midpoint of the third and fourth armsto another of said repeater input terminals, a connection from themidpoint of said first and fourth arms to a repeater output terminal, acon nection from the midpoint of the second and third arms to a secondrepeater output terminal, and means for preventing potentials said firsttwo connections may have to ground due to currents in parallel in saidconnections from being impressed upon said repeater input terminals.

21. A repeating system comprising a unidirectional path containing anamplifier, a Y gain adjusting potent ometer for said ampli- 'fier,connections from the input terminals of said amplifier symmetrically andadjustably connected to points on-said potentiom- Leter, and means forpreventing longitudinal currents in said path from causing saidamplifier to sing.

22. A repeating system comprising a unidirectional path containing anamplifier. a

I gain adjusting potentiometer for said amplifier, connections from theinput terminals of said amplifier symmetrically and adjustably connectedto points on said potentiometer, and a connect-ion to ground from themidpoint of said potentiometer.

23. A repeating system comprising a unidirectional path containing anamplifier, a. gain adjusting potentiometer for said amplifier,connections from the input terminals of said amplifiersymmetrically andadjustably connected to points on said potentiometer, and asymmetricalpath to ground for i a portion of said connections for preventing saidamplifier from singing.

24. Incombination, two line sections, a uni-directionalpat-h betweensaid lines comprising a repeater having input and output terminals, atransformer between one of said lines and said input terminals, a gainadj usting potentiometer, connections from the terminals of the primarywinding of said transformer symmetrically and adjustably connected topoints on'said potentiometer, and a path to ground for said connections.

25. In combination, two line sectio'ns,-a uni-directional path betweensaid lines comprising a repeater having input and output terminals, atransformer between one of said lines and said input terminals, a gainadof said paths, a wave filter in each of said paths for preventing saidrepeaters from singing due to series currents in one of said pathsproduced by potentials in the other of said paths, and means forpreventing said repeaters from singing at a. high frequency due tolongitudinal currents in one of said paths produced by potentials fromthe other of said paths. i

In witness whereof, I hereunto subscribemy namethis 19th day ofNovember, A. D., 1919.

ROBE C. MATHES.

